No description available.

Ferroelectric-reinforced metal matrix composites (FR-MMCs) offer the potential to improve damping characteristics of structural materials. Many structural materials are valued based on their stiffness and strength; however, stiff materials typically have limited inherent ability to dampen mechanical or acoustic vibrations. The addition of ferroelectric ceramic particles may also augment the strength of the matrix, creating a multifunctional composite. The damping behavior of two FR-MMC systems has been examined. One involved the incorporation of barium titanate (BaTiO3) particles into a Cu- 10w%Sn (bearing bronze) matrix and the other incorporating them into an electroformed Ni matrix. Here the damping properties of the resulting ferroelectric reinforced metal matrix composites (FR-MMCs) have been investigated versus frequency, temperature (above and below the Curie temperature of the reinforcement), and number of strain cycles. FR-MMCs currently represent a material system capable of exhibiting increased damping ability, as compared to the structural metal matrix alone. Dynamic mechanical analysis and neutron diffraction have shown that much of this added damping ability can be attributed to the ferroelectric/ferroelastic nature of the reinforcement. / Ph. D.

This research presents a novel microfabrication approach and testing methodology for cylindrical ion trap (CIT) microarray tunable for mass- spectrometers. The growing interest in cylindrical ion trap (CIT) mass-spectrometers is primarily due to ease with which cylindrical geometry can be realized as compared to hyperbolic surfaces found in conventional quadrupole ion traps. Also due to the fact that the potential at the center of hyperbolic electrode in quadrupole ion trap and cylindrical electrode in cylindrical ion trap (CIT) does not differ significantly[2]. Since the RF voltage required to eject a given mass-to-charge ion scales as the square of the ion trap radius, a decrease in ion trap dimensions provides a significant reduction in electronics requirements, thereby providing a pathway for overall system miniaturization. The reduction in sensitivity due to reduced ion storage capacity as a result of miniaturization can be improved by employing an array of identically sized ion traps. Microfabrication approach promises excellent uniformity in the fabrication of identically sized holes which in turn leads to low-cost high performance CIT microarray for mass spectrometers[1,2]. The criterion used for the determination of trap diameter was to ensure that the hole to be 1.09 times the wafer thickness to provide optimal potential to trap ions[1]. The end- plates were designed to optimize the electron and ion transmission into and out of the ion trap and provide a high quality electric field definition within each cylindrical ion trap (CIT)[3]. Two different approaches, namely deep reactive ion etching (DRIE) and mechanical drilling using ultrasonic disc cutter were proposed and used for the fabrication of ring-electrode which forms the main body of the ion trap. Excellent uniformity in hole diameter was observed in both the approaches. The end-plates were fabricated using deep reactive ion etching (DRIE) which provided high transmission rigid grid structure for ions and electrons. Standard Bosch process was used for deep reactive ion etching (DRIE). The two electrodes were metallized using electroless plating which provides excellent uniformity of coating even on end-plate structures with 5micro m through holes. CYTOP[trademark], a cyclized perfluoro polymer, was used as an insulation layer and intermediate bonding layer between the ring electrode and end-plates. The breakdown voltage for a released 16 micro m thick CYTOP[trademark] layer was found to be 1.47KV. An assembly for testing miniature cylindrical ion trap (CIT) was designed and built. An electron impact ionization source was used for generation of ions. Mass selective instability scan was used to selectively eject ions with different mass-to-charge ratio. A cylindrical ion trap (CIT) with 4mm diameter was fabricated and tested for analyte gases such as krypton and xenon.

Electroless plating is a metal deposition technique widely used in the coating industry. It is the method of choice to plate substrates with complex geometries and nonconductive surfaces, such as polymers and ceramics, since it is based on a chemical reduction in solution rather than on an external electrical energy source like the electroplating method. Among others, examples of well-established applications are the electroless deposition of decorative metal coatings such as gold and silver, wear and corrosion resistant nickel coatings, particularly to coat drive shafts, rotors, and bathroom fixtures, as well as the electroless deposition of copper in electronic devices as diffusion barriers and conductive circuit elements. In the academic research, electroless plating is extensively used thanks to its low cost, simple equipment and versatility that allow rapid prototyping. Two common applications are the coating of small particles and the selective plating of flat surfaces. Metal coated ceramic particles are of enormous interest in many scientific fields, e.g. fluorescent diagnostics in biochemistry, catalysis, and fabrication of photonic crystals. Metal coated ceramic nanoparticles and microparticles are also gaining attention as potential candidates in the fabrication of higher quality metal matrix Composites, which is one of the applications addressed by this work. Metal coated ceramic particles are easier to integrate in metal matrix composites, avoiding aggregation caused by the low wettability of the particles by the matrix metal, and are potentially shielded from oxidation and undesired chemical reactions that take place at the interface between the particles and the metal Matrix. Electroless plating is an autocatalytic process, meaning that the deposited metal atoms catalyze the deposition of further metal. In order to achieve the first stable metal seeds on a surface, the latter has to be functionalized. Without this functionalization the metal ions in the electroless plating bath are not reduced or are simply reduced to metal nanoparticles in solution. The traditional activation step for nonconductive surfaces is performed by immersion of the substrate in palladium based solutions, which is very time-consuming and extremely expensive. In particular for nanoparticles, previous work showed that at least 1015 Pd atoms/cm2 are required for a uniform activation of a surface, meaning that in the case of nanoparticles with a surface area of about 100 m2/g are necessary 6.4 g of palladium for each gram of substrate. Assuming a price of about 150 €/g (laboratory scale) for palladium nanoparticles and palladium precursors used for surface activation, it results that the activation of 1 g of nanoparticles costs around 1000 €. Such costs are suboptimal considering the typical production scale, and therefore alternative functionalization methods are desired. In this work, new organic-based functionalization methods based on (3-mercaptopropyl)triethoxysilane to functionalize oxide particles, 3-aminopropylphosphonic acid to activate carbide particles and a substrate-independent method based on the bioinspired polydopamine are developed and investigated in detail, together with the respective electroless plating baths, which often have to be specifically tailored regarding the different reactivity of the different molecules and substrates. Furthermore, in the fabrication of metallic patterns on substrates by electroless plating, new, simple, and cost-effective activation and metal deposition processes are desired. In this work, two new methods are presented, one based on the printing of (3-mercaptopropyl)triethoxysilane by microcontact printing, the other based on the capillary force lithography of polymethylmethacrylate.

Electroless plating is a metal deposition technique widely used in the coating industry. It is the method of choice to plate substrates with complex geometries and nonconductive surfaces, such as polymers and ceramics, since it is based on a chemical reduction in solution rather than on an external electrical energy source like the electroplating method. Among others, examples of well-established applications are the electroless deposition of decorative metal coatings such as gold and silver, wear and corrosion resistant nickel coatings, particularly to coat drive shafts, rotors, and bathroom fixtures, as well as the electroless deposition of copper in electronic devices as diffusion barriers and conductive circuit elements. In the academic research, electroless plating is extensively used thanks to its low cost, simple equipment and versatility that allow rapid prototyping. Two common applications are the coating of small particles and the selective plating of flat surfaces. Metal coated ceramic particles are of enormous interest in many scientific fields, e.g. fluorescent diagnostics in biochemistry, catalysis, and fabrication of photonic crystals. Metal coated ceramic nanoparticles and microparticles are also gaining attention as potential candidates in the fabrication of higher quality metal matrix Composites, which is one of the applications addressed by this work. Metal coated ceramic particles are easier to integrate in metal matrix composites, avoiding aggregation caused by the low wettability of the particles by the matrix metal, and are potentially shielded from oxidation and undesired chemical reactions that take place at the interface between the particles and the metal Matrix. Electroless plating is an autocatalytic process, meaning that the deposited metal atoms catalyze the deposition of further metal. In order to achieve the first stable metal seeds on a surface, the latter has to be functionalized. Without this functionalization the metal ions in the electroless plating bath are not reduced or are simply reduced to metal nanoparticles in solution. The traditional activation step for nonconductive surfaces is performed by immersion of the substrate in palladium based solutions, which is very time-consuming and extremely expensive. In particular for nanoparticles, previous work showed that at least 1015 Pd atoms/cm2 are required for a uniform activation of a surface, meaning that in the case of nanoparticles with a surface area of about 100 m2/g are necessary 6.4 g of palladium for each gram of substrate. Assuming a price of about 150 €/g (laboratory scale) for palladium nanoparticles and palladium precursors used for surface activation, it results that the activation of 1 g of nanoparticles costs around 1000 €. Such costs are suboptimal considering the typical production scale, and therefore alternative functionalization methods are desired. In this work, new organic-based functionalization methods based on (3-mercaptopropyl)triethoxysilane to functionalize oxide particles, 3-aminopropylphosphonic acid to activate carbide particles and a substrate-independent method based on the bioinspired polydopamine are developed and investigated in detail, together with the respective electroless plating baths, which often have to be specifically tailored regarding the different reactivity of the different molecules and substrates. Furthermore, in the fabrication of metallic patterns on substrates by electroless plating, new, simple, and cost-effective activation and metal deposition processes are desired. In this work, two new methods are presented, one based on the printing of (3-mercaptopropyl)triethoxysilane by microcontact printing, the other based on the capillary force lithography of polymethylmethacrylate.

No description available.

In this dissertation, I developed a Pd seeding method in association with electroless plating, to successfully metallize both lambda DNA and DNA origami templates on different surfaces. On mica surfaces, this method offered a fast, simple process, and the ability to obtain a relatively high yield of metallized DNA nanostructures. When using lambda DNA as the templates, I studied the effect of Pd(II) activation time on the seed height and density, and an optimal activation time between 10 and 30 min was obtained. Based on the Pd seeds formed on DNA, as well as a Pd electroless plating solution, continuous Pd nanowires that had an average diameter of ~28 nm were formed with good selectivity on lambda DNA. The selected Pd activation time was also applied to metallize "T"-shape DNA origami, and Au coated branched nanostructures with a length between 200-250 nm, and wire diameters of ~40 nm were also fabricated. In addition, I found that the addition of Mg2+ ion into the reducing agent and electroless plating solution could benefit the surface retention of Pd seeded DNA and Au plated DNA structures. This work indicated that DNA molecules were promising templates to fabricate metal nanostructures; moreover, the formation of Au metallized branched nanostructures showed progress towards nanodevice fabrication using DNA origami. Silicon surfaces were also used as the substrates for DNA metallization. More complex circular circuit DNA origami templates were used. To obtain high enough seed density, multiple Pd seeding steps were applied which showed good selectivity and the seeded DNA origami remained on the surface after seeding steps. I used distribution analysis of seed height to study the effect of seeding steps on both average height and the uniformity of the Pd seeds. Four-repeated palladium seedings were confirmed to be optimal by the AFM images, seed height distribution analysis, and Au electroless plating results. Both Au and Cu metallized circular circuit design DNA origami were successfully obtained with high yield and good selectivity. The structures were maintained well after metallization, and the average diameters of Au and Cu samples were ~32 nm and 40 nm, respectively. Electrical conductivity measurements were done on these Au and Cu samples, both of which showed ohmic behavior. This is the first work to demonstrate the conductivity of Cu metallized DNA templates. In addition, the resistivities were calculated based on the measured resistance and the size of the metallized structures. My work shows promising progress with metallized DNA and DNA origami templates. The resulting metal nanostructures may find use as conducting interconnects for nanoscale objects as well as in surface enhanced Raman scattering analysis.

This thesis describes a new technique for the preparation of ultrathin Pd based membranes supported on a hollow-fiber α-alumina substrate for H₂ separation. The effectiveness of the membranes is demonstrated in the ethanol steam reforming (EtOH SR) reaction in a membrane reactor (MR) for H₂ production. The membrane preparation technique uses an electric-field to uniformly deposit Pd nanoparticle seeds on a substrate followed by deposition of Pd or Pd-Cu layers on the activated surface by electroless plating (ELP). The well distributed Pd nanoparticles allow for enhanced bonding between the selective layer and the substrate and the formation of gas tight and thermally stable Pd or Pd-Cu layers as thin as 1 µm, which is a record in the field. The best Pd membrane showed H₂ permeance as high as 5.0 × 10⁶ mol m²s⁻¹Pa⁻¹ and stable H²/N₂ selectivity of 9000 - 7000 at 733 K for 5 days. The Pd-Cu alloy membrane showed H₂ permeance of 2.5 × 10⁶ mol m⁻²s⁻¹Pa⁻¹ and H₂/N₂ selectivity of 970 at the same conditions. The reaction studies were carried out with a Co-Na/ZnO catalyst both in a packed bed reactor (PBR) and in a MR equipped with the Pd or Pd-Cu membrane to evaluate the benefits of employing membranes. For all studies, ethanol conversion and hydrogen product yields were significantly higher in the MRs compared to the PBR. Average ethanol conversion enhancement and hydrogen molar flow enhancement were measured to be 12 % and 11 % in the Pd MR and 22 % and 19 % in the Pd-Cu MR, respectively. These enhancements of the conversion and product yield can be attributed to the shift in reaction equilibria by continuous hydrogen removal by the Pd based membranes. The comparative low enhancement in the Pd MR was found to be the result of significant contamination of Pd layer by CO or carbon compounds deposition during the reaction. A one-dimensional modeling of the MR and the PBR was conducted using identical conditions and their performances were compared with the values obtained from the experimental study. The model was developed using a simplified power law and the predicted values matched experimental data with only minor deviations indicating that the model was capturing the essential physicochemical behavior of the system. Enhancements of ethanol conversion and hydrogen yield were observed to increase with rise in space velocity (SV), which could be explained by the increase in H₂ flux through the membranes with SV in the MRs. / Ph. D.

This thesis focuses on improving the adhesion of electroless metal layers plated to pit contacts in interdigitated, backside buried contact (IBBC) solar cells. In an electrolessly plated, pit contact IBBC cell, the contact grooves are replaced with lines of pits which are interconnected by the plated metal. It is shown, however, that electroless metal layers, plated by the standard IBBC plating sequence, are not adherent on pit contact IBBC solar cells. The cause of this adhesion problem is investigated by examining the adhesive properties of each of the metal layers in the electroless metallization sequence on planar test structures. This investigation reveals that Pd activation of heavily P diffused Si impedes Ni silicide growth and that, in the absence of a silicide at the Ni/Si interface, an electrolessly plated Cu layer will cause the underlying Ni layer to peel away from the substrate. It is also found that the Ni silicidation process itself intermittently causes the unreacted Ni to spontaneously peel away from the substrate. An electroless metallization sequence that results in thick, adhesive Cu deposits on planar &lt 100&gt surfaces is developed in this thesis. It is shown that this process leads to the formation of a Ni silicide on both n- and p- type, heavily diffused surfaces. Fully plated, pit contact IBBC solar cells were not able to be fabricated during the course of this work but it is reasonable to expect that the modified plating sequence developed in this work will result in the metal layers being adhesive on these cells.

<p>The aim of this study is to synthesize a material with high thermal conductivity and a low coefficient of thermal expansion (CTE), useful as a heat sink. Carbon nanofibres (CNF) are first coated with copper by an electroless plating technique and then sintered to a solid sample by either spark plasma sintering (SPS) or hot pressing (HP). The final product is a carbon nanofibre reinforced copper composite. Two different fibre structures are considered: platlet (PL) and herringbone (HB). The influence of the amount of CNF reinforcement (6-24 %wt), on the thermal conductivity and CTE is studied. CNF has an excellent thermal conductivity in the direction along the fibre while it is poor in the transverse direction. The CTE is close to zero in the temperature range of interest. The adhesion of Cu to the CNF surface is in general poor and thus improving the the wetting of the copper by surface modifications of the fibres are of interest such that thermal gaps in the microstructure can be avoided. The poor wetting results in CNF agglomerates, resulting in an inhomogeneous microstructure. In this report a combination of three different types of surface modifications has been tested: (1) electroless deposition of copper was used to improve Cu impregnation of CNF; (2) heat treatment of CNF to improve wetting; and (3) introduction of a Cr buffer layer to further enhance wetting. The obtained composite microstructures are characterized in terms of chemical composition, grain size and degree of agglomeration. In addition their densities are also reported. The thermal properties were evaluated in terms of thermal diffusivity, thermal conductivity and CTE. Cr/Cu coated platelet fibres (6wt% of CNF reinforcement) sintered by SPS is the sample with the highest thermal conductivity, ~200 W/Km. The thermal conductivity is found to decrease with increasing content of CNFs.</p>